1. Field of the Invention
The invention relates to a method for removing photoresist in a metallization process, and in particular to a method which can completely remove photoresist residue remaining on the surface of a metal layer and avoids corrosion of the metal layer in the metallization process.
2. Description of the Related Art
A method for patterning a metal layer according to the prior art is completed by using photolithography to form a photoresist layer on a metal layer, etching the metal layer toward the photoresist layer and removing the photoresist layer. In this method, there are two main factors which affect the quality of the pattered metal layer. One is that a photoresist residue easily remains on the surface of the metal layer, the other is that the metal layer is corroded. These two factors will be described in detail hereinafter.
As can be seen from the above, the photoresist residue easily remains on the exposed surface of the metal layer in a process of etching the metal layer covered with the photoresist layer before removing the photoresist layer. Since the residue is a macromolecular polymer, it has to be removed.
Furthermore, the metal etching is performed by use of a halide plasma. After etching the metal layer, a metal halide is produced on the exposed surface of the metal layer while halogen ions exist in the remaining photoresist. The halide and halogen ions typically cause metal corrosion.
Now, taking an aluminum alloy layer as an example, the aluminum alloy layer is etched by use of chloride plasma and/or bromide plasma. After etching, AlCl.sub.3 and/or BrCl.sub.3 not exhausted by a vacuum system or chlorine and/or bromine remain(s) on the surface of the aluminum alloy layer. If the residues are not removed, water molecules in the air react with the remaining chlorine or chloride to generate hydrogen chloride (HCl) or with the remained bromine or bromide to generate hydrogen bromide (HBr) after taking the chip out of a RIE reactor.
Furthermore, the HCl formed on the surface of the aluminum alloy layer due to the water molecules in the air reacts with aluminum to generate an AlCl.sub.3 layer. Then, the AlCl.sub.3 layer reacts with the water molecules again. The above-mentioned reactions continuously repeat and corrode the aluminum alloy layer. On the other hand, HBr can also react with aluminum to corrode the aluminum alloy layer. Moreover, if the photoresist is directly removed by a wet strip process without removing the residues, the water involved in the wet strip process can lead to production of HCL and/or HBr, which then corrodes the aluminum alloy layer.
In order to prevent corrosion of the metal, a previous step is taken in which the photoresist is removed by performing a dry strip process with an O.sub.2 plasma. This avoids subsequent metal corrosion caused by halogen ions existing in the photoresist. Thereafter, the photoresist residue remaining on the surface of the metal layer is removed by performing a wet strip process. However, if the O.sub.2 plasma is used for a dry strip process, the photoresist residue oxidizes and becomes an insoluble oxide, such that the photoresist residue cannot be easily removed in the subsequent wet strip process.